The Stovebolt Site Forums The Shop Area Engine Shop Engine knock! It didn't do it before...

OK, so what have I done now? (forehead slap)... I may have to explain my carb rebuild, but this post is going to be way too long anyway. Sorry.

Background: Bought my 51 Chevy 3100 w/ 216 that was supposedly rebuilt years ago by the PO with newly poured babbit bearings and hadn't been driven much (less than 1K miles, I think he said). Between my dad and I, it's probably been driven about 600 miles over the last 8 years.

So, here's the story. The 216 has run fine, but due to various issues I thought it was time to rebuild the carb. I did so and reinstalled it. It didn't start right away so I hit it with some starting fluid. It knocked a bit on startup but the knock went away with oil pressure build up. It warmed up and I adjusted the carb and I thought all was well.

It sat for about a week and I went to start it again. I cranked it and messed with the choke and flooded it. Hit it with starting fluid again to clear things out. It started, but with the same knock...only a bit longer... that went away after oil pressure build up.

Another week and went to start it again, but checked and saw gas squirt down the venturi. But, yup, you guessed it. Had to use the fluid. It started, but the knock stayed! Oil pressure was fine (per the gauge). I turned it off after about 20-30 seconds.

At first, I second guessed myself and thought that maybe I had left my shop rag in the manifold or something, and, well, you know... I took the carb off and noted there seemed to be extra fuel in the manifold just below the carb. Hmmm...
I removed the manifolds and didn't see any sign that I had indeed left a shop rag in there. I removed the valve cover and didn't see anything I would say was out of the ordinary.

The knock sounds almost like it's dieseling...except I'm trying to keep it running, not turning it off. Maybe a rod knocking? It seems to be coming from cylinder 1 or 2 maybe. Did my using starter fluid do something horrible to the engine? I doubt if my carb rebuild was so bad that I poured enough gas down a cylinder as to hydraulic and bend a rod (or did I?).

What have I done now? All I wanna do is drive my truck before winter (sniff, sniff, snivel...).

A couple of thoughts come to mind ;

Starting fluid is bad for your engine , it explodes , rather than burning at a more measurable rate like petrol.

Since it has been sitting for so long , There may be a bent push rod knocking against the block ( try turning them now you have the valve cover off) .

Yep , it just might be a bad rod bearing , going to have to pull the sump to check that.

Get a good tight grip on that can of starting fluid- - - -open the shop door- - - -fling the can as far as you can throw it- - - -now, find the hammered-out rod and replace it. Maybe you haven't bent a rod or scored the crankshaft.
Jerry

I'm trying to think of a reason a motor will only start with starter fluid being associated with rods, valve train issues. Can't come up with one. Starter fluid is only for emergency not for over and over. Since it fires on the fluid, I will guess fuel delivery/carb/bad gas/big vacuum leak problem. That's the hard start. The knock? Don't know, pre ignition/spark knock/exhaust leak snappy sound or deep mechanical sound? (that won't tell me anything, just wanted to sound like an expert)
P.S. I would want to know if just a semi-fine spray of gas down throat will start it also.

Ran good, you rebuilt the carb, it doesn't run good. "It didn't do it before". You are correct to think it's your rebuild and whatever else you did. Check all manifold pipe plugs, connections, fittings and hoses. Then take carb apart again and re read instructions. Sorry to say all this but I've been there so it's OK. On another post a person was warned about the flange gasket covering Rochester B1 vacuum slot/hole in base of carb. Don't know if that applies to 216.

Dusty: I'll try to get out there tomorrow and check the push rods. Better to start simple first...

Hotrod Lincoln: Yeah, you have a great idea there regarding the start fluid. Do you really think I hammered a rod ? Oh, man, I hope not, but thanks, Jerry.


bartamos: The engine sound was more like an ignition knock, but...
I rebuilt the carb in 08 and when I drove it a couple of weeks ago, it stumbled on accel so I decided to rebuild it. I'm pretty sure I did the rebuild OK and matched the gaskets, etc., but hindsight being 20/20 and all, I should've reached for the gas and not the start fluid. I had no idea it could do that kind of damage. I might get another Carter YF anyhow and rebuild again. I spoke to carbking and found out it's a FrankenCarter YF. Of course, I have the knock I have to track down first. Hopefully, it's not terminal

Did you happen to adjust the distributor while troubleshooting?
Advancing the timing too much will cause knocking.

re. starting fluid. Bad stuff. Many folks laugh but once you start using it on an engine it becomes addicted to it. It gets the engine started but makes the existing problem worse.....

One more on the ether, unless you are trying to start a diesel at 47 below zero, there is no need for it. I have seen at least 2 engines ruined with it.

Stovebolt connecting rods are long, and relatively flimsy. It's possible to twist one by simply torquing the wrist pin pinch bolt incorrectly. You might have bent or twisted a rod instead of hammering the Babbit out, but all it takes is a couple of thousandths of extra clearance to make a Babbit rod noisy. A twisted rod makes the piston rotate in the bore as it moves up and down, and causes an oddball piston slap noise.
Jerry

You need to go back into the carb. If it floods & gas runs in the throat something is wrong. It should start up with a couple of pumps of the throttle. The YF carb is tricky to get the diaphragm in correctly. Make shure the float level is right.

If you can get it running without using starting fluid again try pulling one spark plug wire at a time and see if the knock changes sound or disappears. This will work for either a rod or piston but on a Babbitt rod 216 the rod is the weaker link. A further check is to gently rev the engine and hold at a "no load" point which is the point a rod knock usually is the loudest. We use an old Binks high pressure paint gun with gasoline in the cup and set for a very fine mist for starting engines that traditional priming doesn't work and then ONLY after the engine is already turning over. This doesn't flood the engine or wash anything out and if it backfires and ignites the spray release the trigger and flame is out.

I use acetylene instead of ether- - - -just crack the fuel valve of the torch open a little (No Oxygen!) and put the torch tip down the carburetor throat. It's also handy for finding vacuum leaks- - - -much less messy than spray carburetor cleaner!
Jerry

Old dog learned of a new trick today; Thanks!
You are really right on the no oxygen warning, when we were experimenting with different propellants for our potato gun we found that just a TINY puff of O2 mix with the acetylene was all the end cap of the combustion chamber could stand. Standard fuel was AquaNet hair spray but O2 supercharged it also so care was needed.

I've made a few tennis ball cannons with similar fuel mixtures. Lacquer thinner vapor lit off with a spark plug will get the neighbors' attention for a block in all directions. I've also been known to impress the neighborhood kids when we lived in California with a Styrofoam coffee cup and a very lean oxy/acetylene mixture. That one rattled windows in the nearby houses, and the cup disappeared into a cloud of white powder!
Jerry

Just curious. When you started the engine the knock you say went away or did it continue. Is the oil contaminated so the oil pressure at start up takes a minute.check the oil maybe from flooding gas has thined it out.

I can see all of the kids (young and old alike) reading this thread and putting an eye out!
Note to kids: Many of these 'old kids' posting on this thread are inherently irresponsible (present company included), and are lucky to have all of their body parts intact.

"Getting older is inevitable- - - - -but we can be immature all our lives!"

I fully intend to arrive at the Pearly Gates totally worn out, but in 4-wheel drift, yelling "MAN, WHAT A RIDE!"
Jerry

"You are never too old to have a happy childhood"

Potato cannons, carbide cannons and oxy-acetelyne trash bags never get old.

SimS